The terminal block is multi-purposed. A common purpose is to provide connecting points for a user of the parent device to make wire path connections from the power source to the controller and then on to any remote application of the power. Another purpose is to provide such possibilities of branching in the factory assembly of self-contained electrically powered and controlled units.
At the printed circuit board (PCB), probes from special connectors (one for each lead wire), penetrate through holes in the PCB and are soldered in the well-known (wave soldering) manner, at the opposite side of the PCB.
Prior art terminal block typically employ connectors which have screws and clamping washers. When making a connection, it is necessary to strip the insulation from the lead wire conductors, then if working with wires 20 AWG and above, bend the conductors into a hook, unscrew the terminating screw, feed the lead wire conductors into the space where it will be clamped, adjust the conductors to fit snugly around the body of the screw, tighten the screw until good retaining contact is made. When working with smaller insulated lead wires, the prior art terminal blocks typically employ a screw to press a metal edge into the stripped conductors of the lead wire. Some use only a screw.
Operators tend to overstrip insulation from wires so that there is sufficient exposed wire to make a screw-type connection to a terminal block. Exposed wires are subject to corrosion, especially in humid climates, coastal regions which have salt air and in environments where there is moisture.
Another drawback of terminal blocks with screw-type connectors is that in geographic regions that have wide temperature variations, such as in the northeastern United States, the temperature variations cause expansion and contraction of terminal blocks so that the screws become loose over time, destroying the connection to the lead wires.
Terminal blocks currently available feature terminals rigidly supported in the terminal block, which provides little allowance for movement of the terminal probe relative to the terminal block. The rigidity provides the advantage that the pitch between the terminal probes is accurate and immediately fits the (PCB) holes, and is usually UL recognized. A major disadvantage of this design is that the rigidity makes a condition where any vibration, such as from power screwdrivers, or any other maltreatment can damage the solder connections. Even if just one connection is damaged, the whole assembly of the PCB is destroyed. The design is also costly to manufacture.
Terminal blocks having screw type terminals to permit field connections to a PCB are subject to abusive forces directed at the relatively delicate construction of a PCB. The existence of power impact screwdrivers immediately allows the possibility of applying the wrong size tool to the job. Field operators may be apt to use whatever tool is at their disposal, and if that tool is a 12 volt cordless impact wrench, it is going to apply its impacts to the terminal screws, with damaging results. The following is a non-exhaustive list of negative results that may be expected from such treatment. The screw threads will be stripped. Many terminals only have formed and threaded internal threads, with not enough material to withstand impact type screw driving. The small Phillips recess is not strong enough to withstand the impacts and soon wears into a smooth cone. The impact wrench's violent seating causes the driving bit to jump out of the recess and damage the PCB. The impact wrench's violent bit jumping will break the important terminal block shields separating the terminal positions. The vibration causes the solder joints between the terminals and the PCB to fracture and lose reliable connection. The vibration causes the solder joints PCB conductor traces to lift from the substrate. Any accidental knock which hits the terminal block will break the solder joints and the block.